﻿614 
  F. 
  W. 
  Very 
  — 
  Solar 
  Radiation. 
  

  

  tion 
  of 
  solar 
  material, 
  and 
  the 
  photospheric 
  level 
  is 
  determined 
  

   by 
  the 
  depth 
  at 
  which 
  this 
  temperature 
  is 
  attained. 
  Thus 
  in 
  

   low-temperature 
  stars 
  the 
  photosphere 
  may 
  be 
  an 
  ill-defined 
  

   misty 
  layer 
  of 
  great 
  depth, 
  while 
  in 
  hotter 
  stars 
  the 
  limits 
  

   within 
  which 
  molecular 
  structure 
  can 
  exist 
  should 
  be 
  narrower 
  

   and 
  more 
  sharply 
  defined. 
  

  

  All 
  observations 
  in 
  the 
  solar 
  ultra-violet 
  spectrum 
  show 
  a 
  

   great 
  deficiency 
  of 
  energy 
  by 
  comparison 
  with 
  the 
  theoretical 
  

   curve 
  given 
  by 
  the 
  Wien-Planck 
  law. 
  A 
  part 
  of 
  this 
  deficiency 
  

   may 
  be 
  due 
  to 
  the 
  transference 
  of 
  energy, 
  absorbed 
  in 
  the 
  

   numerous 
  Fraunhofer 
  lines 
  of 
  the 
  ultra-violet, 
  to 
  radiators 
  of 
  

   lower 
  temperature* 
  as 
  already 
  explained, 
  but 
  a 
  part 
  must 
  be 
  

   attributed 
  to 
  inadequate 
  evalution 
  of 
  the 
  depletion 
  of 
  short 
  

   waves 
  by 
  the 
  terrestrial 
  atmosphere. 
  

  

  The 
  depletion 
  of 
  ultra-violet 
  radiation 
  in 
  passing 
  through 
  the 
  

   sun's 
  atmosphere 
  is 
  of 
  interest 
  in 
  another 
  way. 
  In 
  this 
  region 
  

   of 
  short 
  waves 
  occur 
  the 
  widest 
  variations 
  of 
  transmissive 
  

   quality 
  in 
  stellar 
  atmospheres. 
  Humphreys 
  has 
  suggestedf 
  

   that 
  the 
  composition 
  of 
  the 
  solar 
  atmosphere 
  itself 
  changes 
  

   from 
  time 
  to 
  time, 
  or 
  between 
  maximum 
  and 
  minimum 
  sun- 
  

   spot 
  epochs, 
  sufficiently 
  to 
  produce 
  a 
  variation 
  in 
  the 
  quality 
  of 
  

   the 
  solar 
  radiation, 
  even 
  though 
  no 
  change 
  occurs 
  in 
  the 
  total 
  

   quantity 
  of 
  energy 
  emitted. 
  The 
  known 
  variation 
  of 
  the 
  solar 
  

   corona 
  in 
  the 
  sun-spot 
  period 
  and 
  the 
  change 
  in 
  the 
  amount 
  of 
  

   coronal 
  dust 
  may 
  produce 
  a 
  slight 
  alteration 
  of 
  transmissive 
  

   quality, 
  but 
  by 
  far 
  the 
  greater 
  part 
  of 
  the 
  change 
  must 
  take 
  

   place 
  in 
  those 
  deeply 
  lying 
  molecular 
  structures 
  in 
  close 
  con- 
  

   tact 
  with 
  and 
  interpenetrating 
  the 
  photospheric, 
  which 
  so 
  

   greatly 
  scatter 
  the 
  shorter 
  waves 
  and 
  deplete 
  them 
  increasingly 
  

   from 
  center 
  to 
  limb. 
  The 
  thorough 
  demonstration 
  of 
  this 
  

   supposed 
  change 
  must 
  be 
  the 
  subject 
  of 
  a 
  lengthy 
  research 
  

   covering 
  an 
  entire 
  11-year 
  period. 
  Founding 
  his 
  hypothesis 
  

   on 
  a 
  few 
  observations 
  by 
  Abbot 
  and 
  Fowle, 
  Dr. 
  Humphreys 
  

   notes 
  that 
  " 
  on 
  examining 
  Wolfer's 
  curves 
  of 
  sun-spot 
  numbers 
  

   it 
  is 
  seen 
  that 
  the 
  days 
  on 
  which 
  Abbot 
  and 
  Fowle 
  found 
  the 
  

  

  * 
  For 
  the 
  relation 
  between 
  absorption 
  and 
  scattering 
  in 
  foggy 
  media 
  at 
  

   high 
  temperatures, 
  see 
  "Radiation 
  through 
  a 
  Foggy 
  Atmosphere" 
  by 
  

   Arthur 
  Schuster 
  (Astrophysical 
  Journal, 
  vol. 
  xxi, 
  p. 
  1, 
  January, 
  1905). 
  

   Were 
  it 
  not 
  for 
  scattering, 
  "we 
  should 
  only 
  obtain 
  the 
  continuous 
  spectrum 
  

   of 
  the 
  background, 
  the 
  medium 
  not 
  affecting 
  the 
  radiation 
  at 
  all" 
  (op. 
  cit., 
  

   p. 
  11). 
  Selective 
  scattering 
  of 
  short 
  waves 
  and 
  prominence 
  of 
  ultra- 
  

   violet 
  absorption 
  lines 
  increase 
  with 
  the 
  condensation 
  and 
  greater 
  internal 
  

   heat 
  of 
  a 
  star 
  because 
  mist 
  particles, 
  whose 
  scattering 
  action 
  is 
  more 
  

   general, 
  are 
  fewer 
  and 
  only 
  molecules 
  remain 
  which 
  scatter 
  short 
  waves, 
  

   while 
  by 
  the 
  dissipation 
  of 
  mist 
  the 
  masking 
  of 
  the 
  gaseous 
  absorption 
  by 
  

   the 
  latter 
  ceases. 
  This 
  test 
  shows 
  that 
  Arcturus 
  is 
  internally 
  hotter 
  than 
  

   Vega 
  (compare 
  F. 
  W. 
  Very, 
  "A 
  Cosmic 
  Cvcle," 
  this 
  Journal 
  (4), 
  xiii, 
  p. 
  52, 
  

   March, 
  1902). 
  

  

  f 
  W. 
  J. 
  Humphreys: 
  "Solar 
  Disturbances 
  and 
  Terrestrial 
  Temperatures," 
  

   Astrophysical 
  Journal, 
  vol. 
  xxxii, 
  p. 
  97, 
  Sept. 
  1910. 
  

  

  